Embodiments of the invention relate generally to a circuit comprising at least two electronic switches which are electrically coupled in series and where the circuit is capable of synchronously switching the at least two electronic switches.
AC motors are commonly supplied with electrical power from a DC supply bus, to the terminals of which there are connected the different phases of the motors via an inverter which is constituted by switch units whose state is controlled by an appropriate control system.
For example, for high power pump or compressor motor drives, large amount of electrical power is converted by the switch units to provide the electrical energy for the motor drives. Typically, the switch units are constituted by multiple transistors of the insulated gate bipolar transistor (IGBT) type for example. For avoiding damaging the IGBTs because of the high levels of electrical power, it is advantageous to couple in series at least two IGBTs as a single switch unit such that the voltage stress of the series connected IGBTs can be reduced.
The at least two IGBTs which are thus coupled in series should be controlled with complete synchronization so that they correspond to a single switch unit in terms of function. Synchronization errors between IGBTs result in the excessive voltage sustained by only one of the IGBTs, which may bring about the damage thereof. Taking into account the production tolerances of the IGBTs and the precision of the control system, the synchronization of the operation of the IGBTs is difficult to be achieved. Sophisticated electronic control solutions have been developed, however, these solutions require the use of specific integrated circuits which are very costly and complex.
For these and other reasons, there is a need for simpler and low cost circuit designs which are capable of synchronously switching.